Washington (CNN)Oil tycoon and conservative mega-donor Charles Koch had kind words for both Bill and Hillary Clinton in an interview Sunday, saying there was an outside chance he could support her in November.

"We would have to believe her actions would be quite different than her rhetoric. Let me put it that way," he said on ABC's "This Week" Sunday. "But on some of the Republican candidates we would -- before we could support them, we'd have to believe their actions will be quite different than the rhetoric we've heard so far."

Earlier in the interview, Koch said Bill Clinton was better than George W. Bush on issues of economic growth and government spending but did not offer a full-throated endorsement of either Clinton.

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Koch and his brother, David, have been prolific funders of conservative groups and instrumental in the growth and sustenance of the tea party movement. They have also been perhaps the most consistent antagonists for Democrats during all eight years of President Barack Obama's tenure.

And Clinton herself has often fired away at the Kochs.

As recently as last month, Clinton tied her Democratic opponent, Bernie Sanders, to the Koch brothers for his opposition to the Export-Import bank, something the brothers have made a key issue for conservatives.

"I just think it's worth pointing out that the leaders of the fossil fuel industry, the Koch brothers, have just paid to put up an ad praising Sen. Sanders. You know, there are a lot of different powerful interests in Washington. I've taken them on," Clinton said at last month's Democratic debate in Miami, shortly before the Florida primaries.

But Charles Koch has blasted Republican front-runner Donald Trump throughout the Republican contest. He kept up the fire Sunday, when he compared Trump's call to create a Muslim registry to Nazi Germany.

"I mean, this isn't Nazi Germany. I mean, that's monstrous as I said at the time. So, obviously we totally oppose that," Koch told ABC.

The Kochs have long been conservative stalwarts, but not always aligned with the Republican Party. David Koch ran as the vice presidential nominee for the Libertarian Party in 1980. And Charles Koch became a vocal critic of the Iraq War during Bush's tenure.